Mauganh17,
I used them at Spring Fever on thursday when the wind was blowing and the sun was shining, etc, etc.
I was hit hit by gusts, while on the wire, hard enough to cause me to dump the main and I had no problems with the blocks.
As I said, a singlehanded boat does not have as much righting moment as a doublehander.
The boat dumps the wind power (mainsheet load)instead of driving through it.
I would not use these blocks on a Nacra 6.0 for example.

Jim,
Yes, the cleat is flipped over, releasing down.